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Bacteria:
The High G + C Gram Positives
Chapter 24
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Actinomycetes
• Source of most of currently used
antibiotics
• Also produce metabolites that are
anticancer, antihelminthic and
immunosuppressive
• Complex life cycle
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Life Cycle of Actinomycetes
• Filamentous cells (hyphae) and spores
• Hyphae can form branching network
– can grow on surface of substrate or into it to
produce a substrate mycelium
– some hyphae differentiate to form an aerial
mycelium which extends above substratum
• form exospores which are called sporangiospores if
they are located in a sporangium
– at this stage forms secondary metabolites some
of which are medically useful
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aerial hyphae
substrate mycelium
Figure 24.2
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Actinomycetes…..
• spores
– most not heat resistant but withstand
desiccation
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other characteristics used in
actinomycete taxonomy
• morphology and color of the mycelium
and sporangia
• surface features and arrangement of
spores
• % GC in DNA
• cell membrane phospholipid composition
• heat resistance of spores
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Ecological Significance of
Actinomycetes
• Widely distributed in soil (e.g. genera
Arthrobacter, Nocardia, Frankia, and
Streptomyces)
• Play important role in mineralization of
organic matter
• Source of many antibiotics e.g.
Streptomycin, Rifamycins, Lincomycin
• A few are pathogens: e.g. Corynebacterium
diphtheriae, Mycobacterium sp.(bovis,
tuberculosis, leprae)
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Figure 24.3
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Phylum Actinobacteria
• Actinomycetes and other high G + C
gram-positive bacteria
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Table 24.3
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Genus Actinomyces
• Straight or slightly curved rods and slender
filaments with true branching
– may have swollen, clubbed, or clavate ends
• Facultative or obligate aerobes
– require CO2 for best growth
• Normal flora of mucosal surfaces (especially
oral cavity) of humans and other animals
– e.g., A. bovis – lumpy jaw in cattle
– e.g., A. israeli – most important human pathogen
• actinomycoses – ocular disease and periodontal
disease in humans
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Figure 24.6
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Suborder Corynebacterineae
• Has seven families with many known
genera such as
– Corynebacterium
– Mycobacterium
– Nocardia
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Corynebacterium
• Some are harmless soil and water
saprophytes
• Many are animal and human pathogens
– e.g., C. diphtheriae - diphtheria
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Corynebacterium diphtheriae
• after snapping
division bacteria
often remain
partially attached
resulting in
palisade
arrangements of
cells
Figure 24.9
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Genus Mycobacterium
• Straight or slightly curved rods,
sometimes branch or form filaments
• Aerobic and catalase positive
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Figure 24.10
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Mycobacterial cell walls
• Contain waxes with 60 to 90 carbon
mycolic acids
• Acid-fast
– basic fuchsin dye cannot be removed
from cell by acid alcohol treatment
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Figure 24.11
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Important species of
Mycobacterium
• M. bovis – tuberculosis in cattle and
other ruminants
• M. tuberculosis – tuberculosis in
humans
• M. leprae – leprosy
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Genus Nocardia
• Develop a substrate mycelium that
readily breaks into rods and coccoid
elements
• Some also form an aerial mycelium
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Nocardia
Figure 24.12
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Nocardia….
• Most are free-living saprophytes
– can degrade many molecules
• e.g., petroleum hydrocarbons, detergents,
benzene
• involved in biodegradation of rubber joints in
water and sewage pipes
• Some are opportunistic pathogens
causing nocardiosis
– usually infect lungs; can infect central
nervous system
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Streptomycetes
• Are 1 to 20% of culturable soil
microbiota
– produce geosmin
• volatile substance that is source of moist earth
odor
– important in mineralization process
• aerobically degrade many resistant substances
(e.g., pectin lignin, and chitin)
• Produce vast array of antibiotics
• Most are nonpathogenic saprophytes
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Streptomyces
• Aerial hyphae that divide in single
plane to form chains of 3-50
nonmotile spores
• G+C DNA content is 69-78%
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Figure 24.16
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Figure 24.17
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Pathogenic streptomycetes
• Streptomyces scabies
– scab disease in potatoes and beets
• Streptomyces somaliensis
– actinomycetoma
• infection of subcutaneous tissues in
humans
• leads to swelling, abscesses, and bone
destruction
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